In recent years, high resolution NMR spectroscopy has developed into a second method, alongside X-ray crystallography, for determination of the 3D structures of biological macromolecules. Technological advances, both in the development of powerful multi-dimensional NMR experiments and of high-field (up to 14 Tesla) spectrometers, have steadily increased the molecular weight limits for NMR structural studies. However, many important problems in structural biology remain inaccessible using current techniques and spectrometers. There is clearly a need for both new experiments and higher field spectrometers. This proposal requests funding to support the purchase of a 17.6 Tesla (750 MHz 1H frequency) NMR spectrometer for studies of the structure and dynamics of proteins and nucleic acids. The biomolecular NMR group in the Department of Molecular Biology is currently staffed-by 6 senior personnel, 27 postdoctoral fellows, and 3 graduate students. Research activities include both development of new and improved NMR methods and applications of NMR to challenging problems of fundamental importance in structural biology. Many of our ongoing projects are pushing the limits of what is currently possible using existing NMR methodology and spectrometers. Higher magnetic fields give increased resolution and sensitivity, both of which are important in extending the NMR method to systems of higher molecular weight and greater complexity. Based on our experience with 500 and 600 MHz spectrometers, the increased sensitivity and dispersion of the 750 MHz instrument will have a significant impact on our ability to solve many problems. The increased dispersion will probably be most important for systems which cannot be labeled with 15N or 13C and for which homonuclear 1H NMR experiments must be used; examples of such systems include peptide models of protein folding intermediates, protein molten globule states, and DNA Holliday junctions. For some systems, such as multiple zinc finger proteins, protein-DNA complexes and RNA, both isotope labeling and the high dispersion of the 750 MHz spectrometer are likely to be of great importance. The increased sensitivity of the instrument will also be particularly beneficial for projects which are limited to concentrations of lmM or less due to problems of solubility or aggregation.